Method of coating metal surface with an alkyd resin-aminoplast composition



United States Patent fihce Patented Feb. 27, 1968 7 Claims. (Cl. 117-75)ABSTRACT OF THE DESCLOSURE Coating compositions based upon combinationsof alkyd resins and aminoplast resins, modified to improve theiradhesion to metal substrates by the addition of an ungelled adduct of apolymer containing free hydroxyl groups and an anhydride of adicarboxylic acid. The addition can be made to the coating compositionitself or by applying the adduct to the metal surface and subsequentlyapplying the alkyd resin-aminoplast resin composition.

This application is a division of applicaton Serial No. 355,925, filedMar. 30, 1964, now US. Patent 3,329,739.

This invention relates to a method of applying coating compositionsbased upon alkyd resin-aminoplast resin compositions to improve theiradhesion to metal substrates.

Coating compositions based upon a combination of an alkyd resin and anaminoplast resin are well known and have been widely used to providehard and attractive coatings on various articles, such as appliances,automobiles, and the like. Being based upon a combination of two different resinous materials, they achieve properties which cannot beattained using either component alone. For this same reason, however,certain of theless desirable properties of the individual components arefound in compositions based upon their blends.

One of the properties of alkyd-aminoplast compositions which is thus notentirely satisfactory is the adhesion of such compositions to metalsurfaces. Combinations of alkyd resin and aminoplast resin do not adhereto such surfaces to the same extent as compositions based upon alkydresins alone. In many cases, in order to achieve satisfactory adhesionto metal substrates, pretreatment of the metal is required, as byphosphating or the like, or a primer is necessary. This is especiallytrue in compositions containing substantial proportions of theaminoplast resin, for example, percent to 60 percent by weight basedupon the total of the alkyd resin and the aminoplast resin. Compositionscontaining high proportions of aminoplast resin are particularlydesirable in finishes for appliances and similar articles.

It has now been found that the adhesion of alkyd resinarninoplast resincoating compositions to metal surfaces is greatly improved by theaddition of a relatively small amount of an ungelled adduct of a polymercontaining free hydroxyl groups and an anhydride of a dicarboxylic acid.Such adducts are formed by reaction of the anhydride with at least someof the free hydroxyl groups in the hydroxyl-containing polymer. Thecompositions thus produced can be formulated and pigmented in the usualmanner employed with alkyd resin-aminoplast resin coating compositions.The heat-convertible coatings made therefrom have all the outstandingproperties normally associated with such coating materials and, inaddition, provide greatly improved adhesion to metal surfaces. Theadhesion is such that in many instances no pretreatment of the metal orprimer coating is required, even when substantial proportions of theaminoplast resin are prescut.

The alkyd resin-amionplast resin coating compositions to which theinstant invention is applicable include those containing variousaldehyde condensation products of melamine, urea, and similar compounds.Generally, the aminoplast resins form from about 5 percent to about 60percent by weight of the total of the alkyd resin and aminoplast resin.

Arninoplast resins produced from melamine or urea are most common andare preferred. However, condensation products of other amines and amidescan also be employed, for example, those of triazines, diazines,triazoles, guanidines, guanamines, and alkyl and aryl substitutedderivatives of such compounds, including alkyl and aryl substitutedureas, and alkyl and aryl substituted melamines, provided at least oneamino group is present. Some examples of such compounds areN,N-dimethylurea, benzyl urea, dicyaniamide, formoguanamine,acetoguanamine, benzoguanamine, ammeline, 2-chloro-4,6-diamino-1,3,5-

triazine, 6 methyl 2,4 diarnino 1,3,5 triazine, 2-'

phenyl 4 amino 6 hydroxy 1,3,5 triazine, 3,5 diaminotriazole, triamonopyrimidine, 2 mercapto 4,6 diaminopyrimidine, 2,4,6 trihydrazine 1,3,5triazine, 2,4,6 triethyltriamino 1,3,5 triazine, 2,4,6triphenyltriamino-l,3,5-triazine, and the like.

The aldehyde is most often formaldehyde although similar condensationproducts can be made from other aldehydes, such as acetaldehyde,crotonaldehyde, acrolein, benzaldehyde, furfural, and others.

These aldehyde condensation products contain methylol or similar alkylolgroups, the structure of the alkylol group depending upon the particularaldehyde employed. At least a portion, i.e., all or part, of thesealkylol groups may be ctherified by reaction 'with an alcohol to provideorganic solvent-soluble coatings. Any monohydric alcohol can be employedfor this purpose, including such alcohols as methanol, ethanol,propanol, butanol, pentanol, hexanol, heptanol, and other alkanols,usually having up to about 12 carbon atoms, as well as benzyl alcoholand other aromatic alcohols; cyclic alcohols, such as cyclohexanol;monethers of glycols, such as the Cellosolves and Carbitols; andhalogen-substituted or other substituted alcohols, such as3-chloropropanol.

The amine-aldehyde resin is produced in a manner Well known in the art,using acidic or basic catalysts and vary ing conditions of time andtemperature in accordance with conventional practice. The formaldehydeis often employed as a solution in water or alcohol, and thecondensation, etherification and polymerization reactions may be carriedout either sequentially or simultaneously.

Alkyd resins made from saturated oils or saturated fatty acids arepreferred in formulating the compositions of the invention. However,there may be employed any of the saturated or unsaturated alkyd resinsutilized in the coatings field, produced from any polybasic acid andpolyfunctional alcohol. Thus, for example, the alkyd may be made fromsuch polyfunctional acids as phthalic acid, maleic acid, fumaric acid,isophthalic acid, succinic acid, trimellitic acid, adipic acid, azelaicacid, sebacic acid, linoleic acid, fatty acids, and the like, as well asfrom anhydrdes of such acids. The polyfunctional alcohol 'can be, forexample, glycerine, trimethylolethane, trimethylolpropane,pentaerythritol, sorbitol, mannitol, ethylene glycol, diethylene glycol,2,3-butylene glycol, and similar polyols.

The alkyd resin may be oil-modified or non-oilmodified. The oil, whenone is utilized, is preferably coconut oil .or other saturated oil,although drying or semidrying oils, such as fish oils, linseed oil,soybean oil or the like, can also be employed. If desired, the alkydresin can contain a monobasic acid, such as benzoic acid, or a similarmonobasic aromatic acid. The alkyd can also be a polyester containingadipic acid or a similar acid along with various glycols and/ orpolyols.

Included within the scope of the term alkyd resin as used herein arereaction products of polybasic acids and polyfunctional alcohols asdisclosed above, which are copolymerized with one or more otherpolymerizable ethylenically unsaturated monomers. Such monomers includeesters of acrylic acid and methacrylic acid, acrylonitrile, olefinichydrocarbons, and other such monomers containing a CH =C group.

The present invention relates to blends or mixtures of such alkydresin-aminoplast resin compositions with an adduct of ahydroxyl-containing polymer and a carboxylic acid anhydride. Anypolymeric material containing only a few or many free hydroxyl groupsalong the polymer chain. can be utilized in the formation of suchadducts. The following are typical examples of such hydroxylcontainingpolymers.

Polymers of an unsaturated primary aliphatic alcohol with at least onemonomer containing a CH C group: One particularly useful product of thistype is a polymer of allyl alcohol and styrene having the followingPreferably, the value of n is in the range of about 4 to 10, and severalproducts of this general class are available commercially. In thepreparation of such polymers, the allyl alcohol can be replaced by otheralcohols containing a polymerizable CH C group, for example, methallylalcohol, and the like, with aliphatic unsaturated alcohols containing upto about carbon atoms being particularly useful. The monomeric materialwhich is polymerized with the unsaturated alcohol to form the materialsof this class may be selected from the group of polymerizableethylenically unsaturated monomeric materials set forth hereinabove,with styrene and acrylonitrile being particularly preferred. Anotherroute to this type of polymer is through the hydrogenation of acroleincopolymers.

B. Polyesters prepared by the reaction of polyols with polycarboxylicacids: When polyols such as ethylene glycol, propylene glycol,diethylene glycol, or the like glycols and other polyols containing fromabout 2 to 12 carbon atoms are reacted, preferably in excess, with adicarboxylic acid (or anhydride) such as adipic acid, succinic acid,maleic acid, fumaric acid, phthalic acid, isophthalic acid,tetrachlorophthalic acid, .or other 'dicarboxylic acids containing up toabout 12 carbon atoms, there is obtained a polyester having freehydroxyl groups attached to thepolymer chain. Such polyesters may alsobe reacted with anhydrides of carboxylic acids to form the adductsutilized in preparing the compositions of this invention.

C. Polyethers prepared, for example, by the reaction of a polyol such assucrose, sorbitol, glycerol, or the like, containing up to about 10carbon atoms, with an alkylene oxide such as ethylene oxide, propyleneoxide, butylene oxide, or the like, or a mixture of such oxides, canalso contain free hydroxy groups When the polyol component is present inexcess. The resulting hydroxyl-containing polyethers may also be reactedwith anhydrides and carboxylic acids to form adducts which can beblended with alkyd-aminoplast compositions in accordance with thepresent invention.

D. Dolymers containing recurring vinyl alchol units of the structure:

The hydroxyl groups in the polyvinyl alcohol react readily withcarboxylic acid anhydrides such as maleic anhydride to from adductswhich can be employed herein.

E. Hydroxyl-modified vinyl halide polymers: These polymers arepreferably copolymers of a vinyl halide, such as vinyl chloride or vinylbromide, with a vinyl ester of an aliphatic monocarboxylic acid, such asvinyl acetate, vinyl propionate, vinyl butyrate, or the like, whichpolymers are modified by having hydroxyl groups introduced into thecopolymer chain by hydrolysis of at least a portion of the esterlinkages in the copolymer structure. Carboxylic acid anhydrides reactwith such hydroxyl groups to form adducts useful for blending withalkydarninoplast compositions.

F. Epoxide resins: Many of the epoxide resins are reaction products ofepihalihydrins, such as epichlorohydrin, with dihydric phenols, such asbis(4-hydroxyphenyl)-2,2-propane. Some of these materials possesshydroxyl groups along the epoxide polymer structure. These hydroxylgroups may also be reacted with carboxylic acid anhydrides to formadducts; however, care must be taken in the reaction to prevent curingof the epoxide resin by the anhydrid'e.

While the above classes of polymers are representative of those whichmaybe employed in forming the compositions of this invention, they by nomeans represent all of the hydroxy-containing materials which may beused. For example, it is possible to utilize silicon-containing polymerswhich possess free hydroxyl groups.

Any dicarboxylic acid anhydride may be reacted with thehydroxyl-containing polymer to form the adducts utilized. Maleicanhydride is particularly preferred because of its low cost and readyavailability; however, other anhydrides, such as itaconic anhydride,succinic anhydride, adipic anhydride, and other saturated andunsaturated dicarboxylic acid anhydrides, containing about 12 carbonatoms may be used with good results.

In preparing adducts of the free hydroxyl-containing polymers with thedicarboxylic acid anhydrides care should be taken so as to preventsubstantial esterification beyond the opening of the anhydride ring.Unless reaction of the carboxyl groups with the hydroxyl groups isminimized, gelation will take place because of the polyfunctional natureof the reactants. In order to prevent this gelation, therefore, thetemperature of the reaction should be kept as low as possible, forexample, below about 100 C.

One preferred method of carrying out the adduct formation involvesadmixing the hydroxyl-containing polymer and the dicarboxylic acidanhydride in a solvent and refluxing the resulting solution for a periodsufiicient to form the desired adduct, ordinarily 5 to 10 hours. Whileuseful products can be obtained when all of the free hydroxyls of thepolymer are reacted with the dicarboxylic acid anhydrides, the reactionis preferably car ried to a stage where about 20 percent to percent ofsuch hydroxyls are reacted, and it is particularly preferred that theadduct contain about 40 percent to 60 percent of the hydroxyls inunreacted form. The acid number of the adduct solids should ordinarilybe in the range of about 20 to 200 and the hydroxyl value in a range ofabout 40 to 200.

Set forth below are several illustrative examples of the preparation ofadducts of dicarboxylic acid anhydrides with free hydroxyl-containingpolymeric materials.

EXAMPLE A Parts by weight Allyl alcohol-styrene oopolymer (Shell X-450),OH equivalent per 100 grams, 0.45; hydroxyl groups The above componentswere refluxed until the product had an acid value of 60-64 (about 4 to 8hours). The product was then diluted to 50 per cent solids with toluene,the resulting resinous product having the following analysis:

Solids, percent 50 Hydroxyl value 65.0 Acid value 42.0 Viscosity(Gardner-Holdt) E-F EXAMPLE B Example A was repeated, substitutingsuccinic anhydride for the maleic anhydride of the example. The reactionwas carried out in such a way as to react the succinic anhydride withabout 40 percent of the available hydroxyl groups of the allylalcohol-styrene copolymer. The resulting product had a Gardner-Holdtviscosity of W and an acid value of 41.0.

EXAMPLE C In this example, maleic anhydride was reacted with a polyetherobtained by the reaction of sucrose with ethylene oxide in an amountsuch that the maleic anhydride reacted with 40 percent of the availablehydroxyl content of the polyether. The polyether utilized had thefollowing properties:

Hydroxyl value as 461 Solids, percent 99.1 Water, percent 0.115 Ashcontent, parts/million 159 Viscosity, centipoises 27,500

The reaction was carried out in methyl ethyl ketone, the reactionmixture being refluxed for approximately 4 hours, at which time the acidvalue of the product was 79.5 at a 50 percent solids content. TheGardner-Holdt viscosity was A-, and the hydroxyl value was 110.4.

EXAMPLE D Example A was repeated, substituting for the styreneallylalcohol copolymer therein utilized a styrene-allyl alcohol copolymerhaving an equivalent weight in the range of 284-314 and a hydroxylcontent of 5.4 percent to 6.0 percent. The reaction was carried out soas to react about 40 percent of the hydroxyl groups of the polyol withmaleic anhydride. The product had an acid value of 35.2 at 51.8 percentsolids, with a Gardner-Holdt viscosity of W and a hydroxyl value of45.2.

EXAMPLE B EXAMPLE F A polyglycol (Dow 11-100, a propylene oxidecondensate of glycerine having an average molecular weight of 1030) washeated in methyl ethyl ketone at reflux with maleic anhydride. Thereaction was carried out such that about 50 percent of the availablehydroxyl groups in the polyol were reacted with the maleic anhydride.The re- 6 sulting product had a Gardner-Holdt viscosity of A, an acidvalue of 45.9, and a hydroxyl value of 95.

This example was repeated using a polyglycol (Dow 11-300) having amolecular weight of about 4000. When diluted to a solids content of 50.9percent solids with toluene, the product had a Gardner-Holdt viscosityof A, an acid value of 12.48, an a hydroxyl value of 23.85.

EXAMPLE G Maleic anhydride was reacted with a polyester prepared by thereaction of 2 moles of adipic acid,-1 mole of diethylene glycol and 2.2moles of trimethylolpropane. This polyester had an acid value of 1.5 anda hydroxyl value in the range of 350-400. The polyester was dissolved inmethyl ethyl ketone and enough maleic anhydride added to react withabout 40 percent of the hydroxyl groups of the polyester. T 16 mixturewas refluxed until the resulting adduct had an acid value of 97.8 at73.6 percent solids and a Gardner-Holdt viscosity of O.

The coating compositions of this invention are prepared by mixing theforegoing resinous components along with suitable solvents, such asxylene, toluene, butanol, acetone, and the like, and, if desired,pigments or other coloring agents. In many instances, several alkydreisns and several aminoplast resins are included. The adduct of theanhydride and hydroxyl-containing polymer can be added at any time andneed only be thoroughly blended with the other components. The coatingcompositions are applied 'by conventional techniques, such as brushing,rolling or spraying, and are then baked to provide a hard, glossy,adherent coating. Typical baking schedules are from about 20 to 60minutes at 225 F. to 350 F.

The proportion of adduct employed can be varied widely and significantimprovement in adhesion is obtained using as little as 1 percent byweight or even less based upon the total nonvolatile resin solidscontent of the composition. The maximum amount depends upon theparticular alkyd resin and aminoplast resin employed, and the use towhich the coating composition is to be put. As much as 25 percent byweight or more can be used in some cases, but generally, it ispreferable to employ no more than about 10 percent since additionalimprovement using higher amounts are not great and film properties aresometimes adversely affected thereby.

Alternatively, the adduct and the alkyd-aminoplast composition can beapplied separately to the metal surface. This is accomplished byapplying the adduct to the metal surface "and then applying a layer ofthe alkyd resin-aminoplast resin composition. Baking is then carried outas above. When coating the surface in this manner, it has been foundthat optimum proportions of the adduct are applied by dipping the metalsurface into a dilute solution of the adduct in a suitable solvent, suchas that in which it is prepared. The solution preferably contains fromabout 2 percent to about 15 percent by weight of the adduct. Althoughnot always necessary the treated surface is usually air dried for a timesufficent to evaporate the solvent prior to the application of the alkydresin-aminoplast resin composition.

It is considered that the application of the adduct in this manner,while in the nature of a pretreatment for the metal surface, actuallyresults in a blending of an adduct with the alkyd resin-aminoplast resincomposition which is further carried out during the baking of thefinished coating. The results achieved by the use of this method ofapplying the various components are comparable to those attained fromcompositions in which the adduct is blended with the composition priorto application to the metal.

A typical alkyd resin-aminoplast resin enamel employed to demonstratethe instant invention is produced as follows:

A pigment paste is prepared by grinding together 259 parts of titaniumdioxide, 40 parts of xylene, 11 parts of 7 pine oil, and 26 parts of analkyd resin (50 percent nonvolatile resin solids) made from 198 parts ofcoconut fatty acid, 139 parts of glycerol, and 219 parts of phthalicanhydride. This paste is reduced with an additional 37 parts of thealkyd resin, 4 parts of xylene, and 68 parts of butylatedurea-formaldehyde resin (50 percent solids), made from 1.0 mole of urea,2.2 moles of formaldehyde, and 1.73 moles of butanol. In formulating theenamel, the foregoing pigment composition is employed along with theabove urea-formaldehyde resin, a butylated melamineformaldehyde madefrom 1.0 mole of melamine, 6.0 moles of formaldehyde, and 4.3 moles ofbutanol, and a second alkyd resin made from 110 parts of coconut fattyacid, 106 parts of glycerol, 54 parts of para-tertiary butyl benzoicacid, and 192 parts of phthalic anhydride, as follows:

Parts by weight Pigment composition 445 In the above enamel, theaminoplast resins form about 40 percent of the total of the alkyd resinand aminoplast resin present.

The invention was demonstrated by tests such as one in which 100 partsof the above enamel were blended with 3.5 parts of the product ofExample A above. The mixture was then coated on an untreated steel paneland baked for 30 minutes at 250 F. For comparative purposes, a secondpanel was coated with the same enamel, but without the adduct beingadded, and similarly baked. Both panels were then subjected to severaltests, including the conical mandrel flexibility test, ASTM D-522-41,and an impact resistance test using a Gardner Variable Impact Tester.Both these tests are measures of the adhesion of a coating to thesubstrate and indicate properties which are essential to usableprotective coatings.

In other tests, the adduct was applied to the panel prior to theapplication of the enamel. For example, there was made up a percentsolution of the adduct of Example A above in a solvent mixture made upof equal parts of xylene and Cellosolve acetate. An untreated steelpanel was immersed in this solution for 60 seconds and dried at roomtemperature until the solvent had evaporated. There was then applied alayer of the enamel described above and the panel was baked for 30minutes at 250 F. The panel was then subjected to the same testsmentioned above.

It was found that both the panels containing the adduct of Example Aexhibited equivalent properties, and that both were substantiallysuperior in flexibility and impact resistance to the panel containingthe alkyd resin-aminoplast resin composition without the adduct.

Similar results are obtained using other adducts of the class described,such as the adducts of Examples B to G, with the enamel described above,as well as with various other combinations of alkyd resins andaminoplast resins.

According to the provisions of the patent statutes, there are describedabove the invention and What are now considered to be its bestembodiments. However, within the scope of the appended claims, it is tobe understood that the invention can be practiced otherwise than asspecifically described.

What is claimed is:

11. A method of applying an adherent coating of an alkydresin-aminoplast resin coating composition to a metal surface whichcomprises applying to said surface an ungelled adduct of a polymercontaining free hydroxyl groups and an anhydride of a dicarboxylic acid,subsequently applying to said surface a layer of said alkydresin-aminoplast resin coating composition, and baking said layer.

2. The method of claim 1 in which said metal is untreated steel.

3. The method of claim 1 in which said adduct is applied by dipping saidmetal surface into a solution of said adduct and evaporating thesolvent.

4. The method of claim 3 in which said solution contains from about 2percent to about 15 percent by weight of said adduct.

5. The method of claim 1 in which said polymer is selected from thegroup consisting of polymers of an unsaturated aliphatic alcohol,polyesters, polyethers, homopolymers containing recurring vinyl alcoholunits, hydroxyl-modified vinyl halide copolymers and epoxide resins.

6. The method of claim lin which said adduct is an adduct of maleicanhydride and a copolymer of an unsaturated aliphatic alcohol with atleast one other ethylenically unsaturated monomer.

7. The method of claim 6 in which said copolymer is a copolymer of allylalcohol and styrene.

References Cited UNITED STATES PATENTS 2,292,468 8/1942 Oeifinger et al11775 X 2,835,656 5/1958 Unruh et al. 117132 X 2,882,257 4/1959 Hesselet al. 117-132 X 2,915,487 12/1959 Shelley 260850 X 2,937,153 5/1960Rasmussen et al. 117161 X 2,992,132 7/1961 Melamed 117-75 X 3,230,275 1/1966 Sekmakas 260850 X 3,245,954 4/1966 Bergman et al. 260--846 XWILLIAM D. MARTIN, Primary Examiner.

R. HUSACK, Assistant Examiner.

